In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have lead to rapid progress in the field of miniaturization. Typically, these miniaturization techniques involve shortening the wavelength of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays KrF excimer lasers (248 nm) are the main light source used in mass production, and ArF excimer lasers (193 nm) are now also starting to be introduced in mass production. Furthermore, research is also being conducted into lithography techniques that use F2 excimer lasers (157 nm), EUV (extreme ultraviolet radiation), and EB (electron beams) and the like as the light source (radiation source).
Resists for use with these types of short wavelength light sources require a high resolution capable of reproducing patterns of minute dimensions, and a high level of sensitivity relative to these types of short wavelength light sources. One example of a known resist that satisfies these conditions is a chemically amplified resist, which includes a base resin and an acid generator (hereafter referred to as a PAG) that generates acid on exposure, and these chemically amplified resists include positive resists in which the alkali solubility of the exposed portions increases, and negative resists in which the alkali solubility of the exposed portions decreases.
Until recently, polyhydroxystyrene (PHS) or derivative resins thereof in which the hydroxyl groups have been protected with acid-dissociable, dissolution-inhibiting groups (PHS-based resins), which exhibit high transparency relative to a KrF excimer laser (248 nm), have been used as the base resin component of chemically amplified resists. However, because PHS-based resins contain aromatic rings such as benzene rings, their transparency is inadequate for light with wavelengths than shorter than 248 nm, such as light of 193 nm. Accordingly, chemically amplified resists that use a PHS-based resin as the base resin component suffer from low levels of resolution in processes that use light of 193 nm.
As a result, resins that contain structural units derived from (meth)acrylate esters within the principal chain (acrylic resins) are now widely used as base resins for resists that use ArF excimer laser lithography, as they offer excellent transparency in the vicinity of 193 nm.
However, compared with conventional base resins such as the PHS-based resins described above, acrylic resins tend to suffer from inferior etching resistance because of their structure. As a result, various problems may arise, including the development of surface roughness on the resist film surface when dry etching is conducted following resist pattern formation.
Generally, the etching resistance of acrylic resins is improved by techniques such as the use of a polycyclic alicyclic group such as an adamantyl group as a substituent group at the ester portion of the (meth)acrylate ester (for example, see patent reference 1).
However, because replacement of the substituent group has a large effect on the lithography characteristics such as the resolution, optimizing the resin for use as a resist continues to be extremely difficult, and there is also a limit to the level of improvement in etching resistance that can be achieved through replacement of the substituent group.
On the other hand, resins in which the principal chain is formed from polycyclic structural units, such as resins with a polycycloolefin (PCO) skeleton in which the principal chain is formed from structural units derived from polycyclic alicyclic groups such as norbornene, have also been proposed as base resins suitable for use in ArF excimer laser lithography and the like (for example, see patent reference 2). These resins with a PCO skeleton (PCO resins) offer the advantage of exhibiting excellent etching resistance when used as a resist.
However, PCO resins exhibit significantly inferior resolution as compared to acrylic resins. As a result, acrylic resins are most commonly used as the base resins for resists for use with ArF excimer laser lithography.
However, as described above, acrylic resins suffer from reduced etching resistance. Accordingly, a resin that is capable of forming a resist pattern with a high level of resolution and superior etching resistance has been keenly sought as a resin for use within resists.
[Patent Reference 1]
Japanese Patent (Granted) Publication No. 2,881,969
[Patent Reference 2]
Japanese Unexamined Patent Application, First Publication No. 2000-235263